Computer Networking Exam Update 2024 -
2025 | Computer Networking A ctual Exam Latest 2024 Questions and Correct Answers Rated A+ R1. Let's review some of the terminology used in this textbook. Recall that the name of a transport -layer packet is segment and that the name of a link-layer packet is frame. What is the name of a network -layer packet? Recall that both routers and link -layer switches are called packet switches. What is the fundamental difference between a router and link -layer switch? Recall that we use the term routers for both datagram networks and VC networks. -ANSWER -A network -layer packet is a data gram. A router forwards a packet based on the packet's IP (layer 3) address. A link -layer switch forwards a packet based on the packet's MAC (layer 2) address. R2. What are the two most important network -layer functions in a datagram network? What are the three most important network -layer functions in a virtual -circuit network? -ANSWER -The two functions of datagram -based network layer are path determination and switching. The additional function of a vc -based network is call setup. R3. What is the differ ence between routing and forwarding? -ANSWER -
Forwarding is about moving a packet from a router's input link to the appropriate output link. Routing is about determining the end -to-routes between sources and destinations. R4. Do the routers in both datagra m networks and virtual -circuit network use forwarding tables? If so, describe the forwarding tables for both classes of networks. -ANSWER -Yes, both use forwarding tables. For descriptions of the tables, see Section 4.2. R5. Describe some hypothetical serv ices that the network layer can provide to a single packet. Do the same for a flow of packets. Are any of can provide to a single packet. Do the same for a flow of packets. Are any of your hypothetical service provided by the Internet's network layer? Are any provided by ATM's CBR service model? Are any provided by ATM's ABR service model? -ANSWER -... R6. List some applications that would benefit from ATM's CBR service model. -ANSWER -Single packet: guaranteed delivery; guaranteed delivery with guaranteed m aximum delay. Flow of packets: in -order packet delivery; guaranteed minimal bandwidth; guaranteed maximum jitter. None of these services is provided by the Internet's network layer. ATM's CBR service provides both guaranteed delivery and timing. ABR does n ot provide any of these services. R7. Discuss why each input port in a high -speed router stores shadow copy of the forwarding table. -ANSWER -With the shadow copy, the forwarding decision is made locally, at each input port, without invoking the centralize d routing processor. Such decentralized forwarding avoids creating a forwarding processing bottleneck at a single point within the router. R8. Three types of switching fabrics are discussed in Section 4.3. List and briefly describe each type. Which, if an y, can send multiple packets across the fabric in parallel. -ANSWER -Switching via memory; switching via a bus; switching via an interconnection network R9. Describe how packet loss can occur at input ports. Describe how packet loss at input ports can be e liminated (without using infinite buffers). -
ANSWER -Packet loss occurs if queue size at the input port grows large because of slow switching fabric speed and thus exhausting router's buffer space. It can be eliminated if the switching fabric speed is at le ast n times as fast as the input line speed, where n is the number of input ports. R10. Describe how packet loss can occur at input ports. Describe how packet loss at input ports can be eliminated (without using infinite buffers). - ANSWER -Packet loss can occur if the queue size at the output port grows large because of slow outgoing line -speed. R11. What is HOL blocking? Does it occur in input ports or output port? -
ANSWER -HOL blocking - a queued packet in an input queue must wait for transfer through the fabric because it is blocked by another packet at the head of the line. It occurs at the input port. R12. Do router have IP addresses? If so, how many? -ANSWER -Yes. They have one address for each interface. R13. What is the 32 -bit binary equivalent of t he IP address 223.1.3.27? -
ANSWER -11011111 00000001 00000011 00011100 R14. Visit a host that uses DHCP to obtain its IP address, network mask, default router, and IP address of its local DNS server. List these values. -
ANSWER -8 interfaces; 3 forwarding ta bles R15. Suppose there are three routers between a source host and a destination host. Ignoring fragmentation, an IP datagram sent from the source host to the destination host will travel over how many interfaces? How many forwarding tables will be index ed to move the datagram from the source to the destination? -ANSWER -50% overhead R16. Suppose an application generates chunks of 40 bytes of data every 20 msec, and each chunk get encapsulated in a TCP segment and then an IP datagram. What percentage of e ach datagram will be overhead, and what percentage will application data? -ANSWER -The 8 -bit protocol field in the IP datagram contains information about which transport layer protocol the destination host should pass the segment to. R17. Suppose Host A se nds Host B a TCP segment encapsulated in an IP datagram. When Host B receives the datagram, how does the network layer in Host B know it should pass the segment (that is, the payload of the datagram) to TCP rather than a UDP or to something else? -ANSWER - Typically the wireless router includes a DHCP server. DHCP is used to assign IP addresses to the 5 PCs and to the router interface. Yes, the wireless router also uses NAT as it obtains only one IP address from the ISP. R18. Suppose you purchase a wireless router and connect it to your cable modem. Also suppose that your ISP dynamically assign your connected device (that is, your wireless router) one IP address. Also suppose that you have five PCs at home that use 802.11 to wireless connect to your wireless router. How are IP addresses assigned the five PCs? Does the wireless router use NAT? Why or why not? -ANSWER -See Section 4.4.4 R19. Compare and contrast the IPv4 and the IPv6 header fields. Do they have any fields in common? -ANSWER -Yes, because the enti re IPv6 datagram (including header fields) is encapsulated in an an IPv4 datagram R20. It has been said that when IPv6 tunnels through IPv4 router, IPv6 treats the IPv4 tunnels as link layer protocols. Do you agree with this statement? Why or why not? -ANSWER -Link state algorithms: Computes the least -cost path between source and destination using complete, global knowledge about the network. Distance -vector routing: The calculation of the least -cost path is carried out in an iterative, distributed manner. A node only knows the neighbor to which it should forward a packet in order to reach given destination along the least -cost path, and the cost of that path from itself to the destination R21. Compare and contrast link state and distance -vector routing algorithms. -ANSWER -Key: 1.Link -state algorithms is a global routing algorithm, and it requires each node to know the cost of each link in the network. Also, whenever a link cost changes, new link cost must be sent to all nodes. Distance -vector algorithm is a decentralized routing algorithm, and it requires message exchanges between directly connected Neighbors at each iteration. When link costs change ,the DV algorithm will propagate the
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